1. Field of the Invention
This invention relates to a method of making high-purity, large, single crystals which are essentially crack-free.
2. Description of Related Art
Modern electronics has created a demand for high-purity crystalline materials which are the heart of the solid-state electronic systems. The demand for higher purity, larger crystals has increased as the requirements of the electronics systems have become more demanding. One problem encountered in growing such crystals is that the crystal adheres to its container as it is formed. Another problem is that impurities from the container may migrate into the crystal structure during crystal growth. Frequently, the difference in rates of expansion between the crystal material and the container also result in cracking of the container, which is usually a glass tube or crucible.
In one method used in the past, a thin coating of graphite has been deposited on the inner wall of the container. This inert, particulate material prevents migration of material from the wall into the crystal structure. It is also crushable, so that it deforms as the crystal expands. Thus, the expanding crystal will not apply excessive force to the walls of the container which may otherwise cause the container to break. The crystal, however, grows along the length of the container.
The graphite coating may be used in the formation of crystals such as silver gallium selenide, silver indium selenide, silver gallium telluride, cadmium indium telluride, cadmium telluride, and indium telluride. If, however, the desired crystalline material contains sulfur, graphite can react with the sulfur to form carbon disulfide; under the high temperatures used in crystal-forming processes, carbon disulfide may explode. Therefore, the graphite coating is employed with crystalline materials that do not include sulfur.